<!doctype html> 
<html> 
<head> 
    <meta charset="utf-8"> 
    <title></title> 
</head>
<body>

<script type="text/javascript">
	
	var a = 10;
	function show(){
		var a = a + 10;//undefined + 10
		alert(a);//NAN
		return a;//NAN
	};
	alert(a);   //10  //NAN  //NAN //NAN
	//alert(show()+10); 
	alert(show());
	show();
	/*
	var a = new String('');
	a.b = 20;
	alert(a.b)
	/*
	function show(a){
		a.c = 20;
	};
	show(a);
	*/
	//alert(a.c); // 20

</script>
</body>
</html>